Joh’s basic argument was that DNA is fundamentally different than the other detritus we abandon on a regular basis. She contended that, though we might not have an expectation that the soda bottle we tossed into the public trash can won’t be seen by anyone, we have an expectation that it won’t be mined for our saliva and the genetic information it contains. Joh even argued that DNA traces are fundamentally different from fingerprints, since fingerprints can only identify us, but cannot give investigators a view into fundamentals about who we are (including our health risks).

Joh contrasted her view, which focuses on privacy, from what she called the “old” trespass view. Under that perspective, what was wrong about an FBI agent slipping into your house to implant bugs was not that the government could now listen into everything you say in your home, but rather the property violation involved in breaking in. Similarly, under the trespass view, a cop could not run a cotton swab on the inside of your mouth to collect DNA (without a warrant) because it would violate your property in yourself, not because it would reveal your genetic information to the government. But the trespass view would have no problem with the government picking up that soda bottle out of the trash and collecting your DNA from it, to match you to a crime.

Governments have been wary of actively collecting this abandoned DNA, however, and so have gone to great lengths to get suspects to voluntarily send the government their DNA. For example, they’ll ask suspects to mail them information, then get their saliva from the envelope or stamp they licked. Joh is wary of these practices as well.

Joh fears that if we let governments analyze abandoned or given DNA, they might create a national database of DNA, like the present national fingerprint database. Governments may not use this just to identify suspected criminals; they may also mine it for racial data or to study genetic predispositions for criminality.